The invention relates to a fuel injection valve such as is used for example for the injection of fuel into the combustion chamber of an internal combustion engine.
The prior art has disclosed fuel injection valves, such as are used for example for injecting fuel into the combustion chamber of an internal combustion engine. Here, fuel that has been compressed by a high-pressure pump is injected at high pressure directly into a combustion chamber of an internal combustion engine. Here, for the dosing of the fuel, a nozzle needle is used which is arranged in longitudinally displaceable fashion in a housing of the fuel injection valve. Said nozzle needle, by means of its longitudinal movement, opens up one or more injection openings through which the compressed fuel can emerge into the combustion chamber. Owing to the high pressure of the fuel, the fuel is finely atomized in the process, such that an effective combustion of the fuel occurs in the combustion chamber.
The movement of the nozzle needle is controlled by a varying pressure in a control chamber. The control chamber is delimited by that face side of the nozzle needle which is averted from the injection openings, such that the pressure in the control chamber exerts on the nozzle needle a hydraulic closing force which pushes said nozzle needle against a nozzle seat. Hydraulic forces in a pressure chamber which surrounds the nozzle needle and which is filled with highly pressurized fuel during operation exert on the nozzle needle a hydraulic opening force which is directed counter to the closing pressure arising from the hydraulic pressure in the control chamber. If the pressure in the control chamber is lowered, the opening hydraulic pressure on the nozzle needle prevails, and said nozzle needle thereupon moves away from the nozzle seat and opens up the injection openings.
For the adjustment of the pressure in the control chamber, a control valve is used which is formed for example as a magnetic valve, such as is known for example from the laid-open specification DE 10 2007 025 614 A1. The control valve disclosed in said document is constructed as follows: an outflow opening is formed in a valve piece which delimits the control chamber, via which outflow opening fuel can flow out of the control chamber into a low-pressure region, which lowers the pressure in the control chamber. For the opening and closing of the outflow opening, a magnet armature is used which can be moved by means of an electromagnet. Here, the elements within the fuel injection valve are fixed by means of a magnet spring which pushes the electromagnet against the valve piece via a sleeve or some other bracing element. In this way, the parts remain in place during operation, but can nevertheless be easily installed.
The maximum stroke of the magnet armature is determined by the spacing of the valve piece to the electromagnet and is of major significance for two reasons. Firstly, the magnet armature must be able to move over a certain distance in order that the outflow opening opens up an adequately large outflow cross section and thus permits a rapid pressure reduction in the control chamber. Secondly, the spacing of the electromagnet to the magnet armature determines the magnetic force acting on the magnet armature and thus the dynamics of the opening process when the electromagnet is actuated out of its closed position. In the case of the known fuel injection valves having a magnetic valve of said type, however, a situation may arise in which the valve piece is deformed slightly by the pressure in the control chamber. As a result, the seat of the magnet armature on the valve piece moves in the direction of the electromagnet, and thus shortens the maximum stroke of the magnet armature. Correspondingly, the dynamics of the control valve, and thus also the injection dynamics of the fuel injection valve, change, which can have an adverse effect on the control capability and thus on the combustion profile.